1. Field of the Invention
This invention relates to oil well drilling and more particularly to a method and apparatus employing sonic energy for freeing a section of drill string which has become stuck in a bore hole.
2. Description of the Related Art
An ongoing problem in the drilling of oil wells is the sticking of the drill string against the bore hole wall. This problem becomes accentuated where the sticking occurs at a great distance below the surface where the freeing of the string becomes increasingly difficult. Methods and apparatus have been devised in the prior art for employing sonic energy which is fed to the stuck section of the drill pipe to effect its freeing. Such prior art methods and apparatus generally employ mechanical oscillators which are operated at a frequency such as to effect resonant standing wave vibration of the drill string. In U.S. Pat. No. 3,168,140 issued Feb. 2, 1985 to Albert G. Bodine and U.S. Pat. No. 3,155,163 issued Nov. 3, 1964 to Albert G. Bodine, methods and apparatus are described for freeing a drill string in which sonic energy is applied to the top of the drill string to effect resonant standing wave vibration of the string which vibrational energy is fed down the string to the point of sticking. In U.S. Pat. No. 4,667,742 issued May 26, 1987 to Albert G. Bodine, a method and apparatus is described in which the oscillator is lowered down the bore hole and connected to the down hole stuck pipe section and the string then resonantly vibrated to effect the desired freeing action. While some effort is made in all of these prior art devices to vibrationally isolate the drill string from the suspension hardware, either in the form of springs, or by adjusting the frequency of vibration so that a node of the resonant wave appears at the point of connection to the support members, there is no suggestion in these prior art patents of suspending the top of the drill string with a highly elastic support so as to make for very low impedance to the vibrational energy generated by the oscillator at this point. Further, there is no disclosure in such prior art directed to utilizing the drill string as an acoustic lever with the top end of the string being driven with a very high displacement and this high displacement being reflected at the sticking point as a high force vibration.